A recent study published in Nature Communications has examined how symptoms of Long COVID change over a 15-month period after initial infection. The research, conducted by a team analyzing data from the National Institutes of Health (NIH) RECOVER initiative, followed 3,659 adults across 83 sites in the United States, including Washington, DC and Puerto Rico.
The study used the Long COVID Research Index (LCRI), which measures the severity of 11 symptoms on a scale from 0 to 30. A score of 11 or higher was considered indicative of Long COVID. Participants completed symptom surveys at intervals of three, six, nine, twelve, and fifteen months after their first SARS-CoV-2 infection.
Researchers found that at three months post-infection, about 10% of participants met the threshold for Long COVID. At fifteen months, this figure remained similar at nearly 11%. Eight distinct symptom patterns were identified among participants: some experienced persistently high symptom burdens; others had intermittent or improving symptoms; while a smaller group saw worsening or delayed increases in symptoms.
Among those who initially met criteria for Long COVID at three months, most continued to have persistent or fluctuating symptoms through fifteen months. "These findings reveal durable heterogeneity: a persistent-high group, a large intermittently high group, an improving minority, and a small delayed-worsening group, all of which require clinical vigilance," the researchers stated.
Women were more likely than men to experience persistent high symptom burdens. Hospitalization during acute infection was also more common among those with ongoing severe symptoms. Reinfection rates were slightly higher among groups whose symptoms worsened over time but did not fully account for changes in symptom severity.
An uninfected comparison group showed different patterns overall but also included some individuals who reported moderate worsening of symptoms unrelated to COVID-19 infection. The study noted that missing data and loss to follow-up may affect recovery estimates but found consistent results across multiple analyses.
The authors concluded that understanding these varied trajectories can inform clinical care and trial design for Long COVID treatments. "This national prospective analysis shows Long COVID is not a single course but a set of distinct, trackable pathways measurable with the LCRI," they wrote. They suggest that future research should include longer-term monitoring and further investigation into predictive biomarkers and targeted interventions based on observed symptom patterns.
